Cyclestheria hislopi (Crustacea: Branchiopoda): a group of morphologically cryptic species with origins in the Cretaceous

A molecular assessment of species boundaries and relationships in the Australian brine shrimp Parartemia (Anostraca: Parartemiidae)

Australian salt lakes contain a diverse range of endemic invertebrates. The brine shrimp Parartemia is among the most speciose and salt-tolerant of these invertebrates. The morphotaxonomy of Parartemia is well established but there has only been limited molecular assessment of the phylogenetic relationships and boundaries of the morphospecies. We used multiple genetic markers (nuclear 28S and mitochondrial 16S and COI ) and tree-building methods (Bayesian inference and maximum likelihood) to investigate the phylogeny of Parartemia . We also used species delimitation methods to test the validity of morphological species designations. The data set included all but 2 of the 18 described Parartemia morphospecies, collected from a total of 93 sites from across southern Australia plus some sequences from GenBank. The results identified large amounts of molecular divergence (e.g. COI P- values of up to 25.23%), some groups of closely related species (which also usually shared some morphological similarities) and some distinctive species, although the relationships among divergent lineages were generally not well resolved. The most conservative set of results from the species delimitation analyses suggests that the morphotaxonomy is largely accurate, although many morphospecies comprised divergent genetic lineages separated by COI P- values of up to 17.02%. Two putative new morphospecies, three cryptic species and one synonymy were identified. Our findings improve the knowledge of Parartemia taxonomy and will facilitate the development of future studies and conservation of this taxon.

Multi-ocean distribution of a brooding predator in the abyssal benthos

How far are species distributed on the abyssal plains? Spanning from 3000 to 6000 m below sea level, abyssal plains cover three-quarters of the ocean floor and are the largest but also least explored habitat on Earth. The question of vertical and horizontal distribution is central to understanding biogeographic and population genetic processes within species inhabiting the deep-sea benthos. Amphipod crustaceans are an important and dominant taxon in this ecosystem. As they are brooders, their dispersal capacities are more limited compared to species with free-swimming larvae, and with the exception of a few scavenging species deep-sea amphipods are restricted to a single ocean. Based on an integrative taxonomic approach (morphology, COI, 16S and 18S) we demonstrate the occurrence of a predatory amphipod species, Rhachotropis abyssalis, in three oceans: the Antarctic Ross Sea, the Northwest Pacific and the North Atlantic; regions more than 20,000 km apart. Although such extensive geographic distributions may represent a rare exception for brooding predators, these findings might also be no exception at all, but a reflection of the rare sampling and rare taxonomic investigation of invertebrate predators in the deep-sea. Our findings highlight our abysmal state of knowledge regarding biodiversity and biogeography on abyssal plains.

Assigning the Australian clam shrimp Eoleptestheria (Branchiopoda: Spinicaudata: Leptestheriidae) to a new species status

We assign the only Australian leptestherid clam shrimp, Eoleptestheria ticinensis (Balsamo-Crivelli, 1859) to a new species status, Leptestheria timmsi sp. nov., based on the latest molecular phylogeny of spinicaudatan clam shrimps from a previous study. We provide a redescription of the species, highlighting morphological details not explored previously for this species. We also present a comparative account of all Eoleptestheria species and populations throughout the world. The head morphology of Leptestheria timmsi sp. nov. overlaps with other populations of Eoleptestheria and a few Leptestheria species. The telsonic and cercopod marginal spines seem to increase in size posteriorly in L. timmsi sp. nov., unlike in many other Eoleptestheria populations.

Multiple Recent Colonizations of the Australian Region by the Chydorus sphaericus Group (Crustacea: Cladocera)

Biotic introductions are an ongoing disruption for many ecosystems. For passively dispersed freshwater zooplankton, transcontinental introductions have been common but are poorly studied in the southern hemisphere. Here we assess the hypothesis of recent introduction for populations of the Chydorus sphaericus group (Crustacea: Cladocera) in Australia. We analyzed 254 sequences (63 original sequences) from the cytochrome oxidase I region of mitochondrial DNA of Chydorus sp., which included global representation. Three Australian populations were connected with separate clades in the northern hemisphere, suggesting multiple colonization events for Australia. The timescale of the divergences was consistent with recent (Quaternary) dispersal. As Australian populations are exposed to migrating birds from the northern hemisphere, both avian and anthropogenic sources are candidates for dispersal vectors. We concluded that recent cross-hemisphere dispersal in the Chydorus sphaericus group is more common than previously believed.

Aquatic invertebrate community structure and phenology of the intermittent treed swamps of the semi-arid Paroo lowlands in Australia

The middle Paroo lowlands in semi-arid western New South Wales support numerous intermittent wetlands of various types. Differences between them are promoted by three ecological drivers: salinity, turbidity and hydroperiod. Community structure and phenology of the two most common types, saline lakes and claypans, are known but similar ecologies are lacking for the third most common wetland, the treed swamps. These are of six subtypes distinguished by dominant tree species, geomorphology and hydroperiod, all with similar community structure and phenology, but with differing invertebrate diversities. Summed diversity is not as high as in local creek pools, the shorter hydroperiods and simpler geomorphology of the treed swamps being restrictive so that there is almost no replacement of species during the early dominance of branchiopods and later of insects. Such treed swamps are uncommon in the semi-arid zone, but much more speciose treed swamps are known under similar and seasonally dry Mediterranean climates of the Western Australian Wheatbelt where hydroperiods are more stable.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11273-021-09846-0.

Bosminopsis deitersi (Crustacea: Cladocera) as an ancient species group: a revision

Water fleas (Crustacea: Cladocera) of the Family Bosminidae have been studied since the founding of paleolimnology and freshwater ecology. However, one species, Bosminopsis deitersi, stands out for its exceptional multicontinental range and broad ecological requirements. Here we use an integrated morphological and multilocus genetic approach to address the species problem in B. deitersi. We analyzed 32 populations of B. deitersi s. lat. Two nuclear and two mitochondrial loci were used to carry out the bGMYC, mPTP and STACEY algorithms for species delimitation. Detailed morphological study was also carried out across continents. The evidence indicated a widely distributed cryptic species in the Old World (Bosminopsis zernowi) that is genetically divergent from B. deitersi s.str. We revised the taxonomy and redescribed the species in this complex. Our sampling indicated that B. zernowi had weak genetic differentiation across its range. A molecular clock and biogeographic analysis with fossil calibrations suggested a Mesozoic origin for the Bosminopsis deitersi group. Our evidence rejects the single species hypothesis for B. deitersi and is consistent with an ancient species group (potentially Mesozoic) that shows marked morphological conservation. The family Bosminidae, then, has examples of both rapid morphological evolution (Holocene Bosmina), and morphological stasis (Bosminopsis).

Three nuclear protein-coding genes corroborate a recent phylogenomic model of the Branchiopoda (Crustacea) and provide estimates of the divergence times of the major branchiopodan taxa

The class Branchiopoda (Crustacea) shows great diversity in morphology and lifestyle among its constituent higher-level taxa: Anostraca, Notostraca, Laevicaudata, Spinicaudata, Cyclestherida and Cladocera. The phylogenetic relationships among these taxa have long been controversial. We sequenced three orthologous nuclear genes that encode the catalytic subunit of DNA polymerase delta and the largest and second-largest subunits of RNA polymerase II in the expectation that the amino acid sequences encoded by these genes might be effective in clarifying branchiopod phylogeny and estimating the times of divergence of the major branchiopodan taxa. The results of phylogenetic analyses based on these amino acid sequences support the monophyly of Branchiopoda and provide strong molecular evidence in support of the following phylogenetic relationships: (Anostraca, (Notostraca, (Laevicaudata, (Spinicaudata, (Cyclestherida, Cladocera))))). Within Cladocera, comparison of the nucleotide sequences of these same genes shows Ctenopoda to be the sister group of Haplopoda + Anomopoda. Three statistical tests based on the present amino acid sequence data-the approximately unbiased test, Kishino-Hasegawa test and weighted Shimodaira-Hasegawa test-tend to refute most of the previous molecular phylogenetic studies on Branchiopoda, which have placed Notostraca differently than here; however, our results corroborate those of one recent phylogenomic study, thus confirming the effectiveness of these three genes to investigate relationships among branchiopod higher taxa. Divergence time estimates calibrated on the basis of fossil evidence suggest that the first divergence of extant branchiopods occurred about 534 Ma during the early Cambrian period and that diversification within the extant branchiopod lineages started in or after the late Permian.

The Fossil Record of the Clam Shrimp (Crustacea; Branchiopoda)

Clam shrimp (the paraphyletic assemblage of spinicaudatans, laevicaudatans, cyclestherids and the extinct leaiins) are small, bivalved branchiopod crustaceans that specialize in ephemeral freshwater habitats. They have a long fossil record (Devonian onward) that has often been overlooked. Here we briefly review the fossil record of the major groups of clam shrimp and clear up some misconceptions in the literature as to their origin. The dominant group of clam shrimp in the fossil record is the Spinicaudata, which have a diverse fossil record beginning in the Devonian. The clam shrimp suborder Laevicaudata are known from the Permian, with possible soft-part preservation from the Jurassic. However, owing the character-poor nature of these fossils, it is impossible to tell if they represent crown group or stem group laevicaudatans. In contrast, the total group Spinicaudata have a rich record of mostly carapace fossils- the earliest from the Early Devonian. The leaiins are an enigmatic extinct diplostracan lineage thought to be closely related to the spinicaudatans. They have a record that extends from the Middle Devonian to the Permian. The Cyclestherida have a somewhat problematic fossil record: there are no examples of cyclestherids preserved with soft-parts, so the only character used to assign fossils to this lineage is the carapace shape. According to that metric, cyclestherids have a record that begins in the Middle Devonian. Exceptionally preserved clam shrimp are found in the Paleozoic and Mesozoic. Assessing holistically what is known about the clam shrimp fossil record along with carapace morphology, carapace ornamentation and examples of exceptional preservation will ultimately contribute to a synthetic paleontological and neontological understanding of the group, its systematics and evolution.

Distribution of Clam Shrimps (Crustacea: Laevicaudata and Spinicaudata) in South Africa, with New Records from the Northern Cape Province

The ephemeral waterbodies of southern Africa are regarded a global hotspot for large Branchiopod diversity. Although the distributions and systematics of Anostraca and Notostraca have been fairly well defined, clam shrimps have received much less attention. So far, 18 clam shrimp species are known from the sub-region, but none of the available published literature defines their distribution in South Africa. Furthermore, most of the recent studies were concentrated in the mesic provinces, while very little information is available from the Northern Cape, where most ephemeral waterbodies in the country occur. This study reviews the distribution of clam shrimps in South Africa by reviewing published distribution records and contributing novel data from surveys in the Northern Cape. We found that 13 of the 18 species from the sub-region occur in South Africa, of which four are restricted to their respective provinces. We further clarify the current state of endemism patterns in South Africa and provide novel findings from the Northern Cape, including three new range extensions. The Northern Cape hosts the highest species richness, with nine species, followed by the Eastern Cape, where seven species have been recorded so far. Most other provinces have low species richness and endemism, while no species records have been published from the Limpopo province yet. Surveys over large geographical scales are important, and more research is needed on clam shrimp systematics in South Africa.

Phylogeny and Biogeography of Spinicaudata (Crustacea: Branchiopoda)

Spinicaudata (spiny clam shrimp) is a taxon of Branchiopoda occurring since the Devonian and today it occurs nearly globally in temporary water bodies. We present the most species-rich phylogenetic analyses of this taxon based on four molecular loci: COI, 16S rRNA, EF1α and 28S rRNA. Our results support previous findings that Cyzicidae sensu lato is paraphyletic. To render Cyzicidae monophyletic we establish a fourth extant spinicaudatan family to accommodate Eocyzicus. Within Cyzicidae, none of the genera Cyzicus, Caenestheria or Caenestheriella are monophyletic, and the morphological characters used to define these genera (condyle length and rostrum shape) are not associated with well-delimited clades within Cyzicidae. There is insufficient resolution to elucidate the relationships within Leptestheriidae. However, there is sufficient evidence to show that the leptestheriid genera Eoleptestheria and Leptestheria are non-monophyletic, and there is no support for the genus Leptestheriella. Molecular clock analyses suggest that the wide geographic distribution of many spinicaudatan taxa across multiple continents is largely based on vicariance associated with the break-up of Pangea and Gondwana. Trans-oceanic dispersal has occurred in some taxa (e.g., Eulimnadia and within Leptestheriidae) but has been relatively rare. Our results highlight the need to revise the taxonomy of Cyzicidae and Leptestheriidae and provide evidence that the global spinicaudatan diversity may be underestimated due to the presence of numerous cryptic species. We establish Eocyzicidae fam. nov. to accommodate the genus Eocyzicus. Consequently, Cyzicidae comprises only two genera -Cyzicus and Ozestheria. Ozestheria occurs also in Africa and Asia and Ozestheria pilosa new comb. is assigned to this genus.

A new species group from the Daphnia curvirostris species complex (Cladocera: Anomopoda) from the eastern Palaearctic: taxonomy, phylogeny and phylogeography

The eastern Palaearctic is a centre of diversity for freshwater cladocerans (Crustacea), but little is known about the evolution and taxonomy of this diversity. Daphnia curvirostris is a Holarctic species complex that has most of its diversity in the eastern Palaearctic. We examined the phylogeography, rates of evolution and taxonomic status for each clade of the D. curvirostris complex using morphological and genetic evidence from four genes. The cybertaxonomical and morphological evidence supported an eastern Palaearctic clade, with at least four species (described here as the Daphnia korovchinskyi sp. nov. group) having diagnostic morphological characters. We also detected convergent morphological characters in the D. curvirostris complex that provided information about species boundaries. Two of the new species (Daphnia koreana sp. nov. and Daphnia ishidai sp. nov.) are known from single ponds and are threatened by human activity. Divergence time estimates suggested an ancient origin (12–28 Mya) for the D. korovchinskyi group, but these estimates are complicated by the small number of calibration points.

Phylogeography of Daphnia magna Straus (Crustacea: Cladocera) in Northern Eurasia: Evidence for a deep longitudinal split between mitochondrial lineages

Species with a large geographic distributions present a challenge for phylogeographic studies due to logistic difficulties of obtaining adequate sampling. For instance, in most species with a Holarctic distribution, the majority of studies has concentrated on the European or North American part of the distribution, with the Eastern Palearctic region being notably understudied. Here, we study the phylogeography of the freshwater cladoceran Daphnia magna Straus, 1820 (Crustacea: Cladocera), based on partial mitochondrial COI sequences and using specimens from populations spread longitudinally from westernmost Europe to easternmost Asia, with many samples from previously strongly understudied regions in Siberia and Eastern Asia. The results confirm the previously suspected deep split between Eastern and Western mitochondrial haplotype super-clades. We find a narrow contact zone between these two super-clades in the eastern part of Western Siberia, with proven co-occurrence in a single lake in the Novosibirsk region. However, at present there is no evidence suggesting that the two mitochondrial super-clades represent cryptic species. Rather, they may be explained by secondary contact after expansion from different refugia. Interestingly, Central Siberia has previously been found to be an important contact zone also in other cladoceran species, and may thus be a crucial area for understanding the Eurasian phylogeography of freshwater invertebrates. Together, our study provides an unprecedented complete, while still not global, picture of the phylogeography of this important model species.

Unraveling the origin of Cladocera by identifying heterochrony in the developmental sequences of Branchiopoda

INTRODUCTION

One of the most interesting riddles within crustaceans is the origin of Cladocera (water fleas). Cladocerans are morphologically diverse and in terms of size and body segmentation differ considerably from other branchiopod taxa (Anostraca, Notostraca, Laevicaudata, Spinicaudata and Cyclestherida). In 1876, the famous zoologist Carl Claus proposed with regard to their origin that cladocerans might have evolved from a precociously maturing larva of a clam shrimp-like ancestor which was able to reproduce at this early stage of development. In order to shed light on this shift in organogenesis and to identify (potential) changes in the chronology of development (heterochrony), we investigated the external and internal development of the ctenopod Penilia avirostris and compared it to development in representatives of Anostraca, Notostraca, Laevicaudata, Spinicaudata and Cyclestherida. The development of the nervous system was investigated using immunohistochemical labeling and confocal microscopy. External morphological development was followed using a scanning electron microscope and confocal microscopy to detect the autofluorescence of the external cuticle.

RESULTS

In Anostraca, Notostraca, Laevicaudata and Spinicaudata development is indirect and a free-swimming nauplius hatches from resting eggs. In contrast, development in Cyclestherida and Cladocera, in which non-swimming embryo-like larvae hatch from subitaneous eggs (without a resting phase) is defined herein as pseudo-direct and differs considerably from that of the other groups. Both external and internal development in Anostraca, Notostraca, Laevicaudata and Spinicaudata is directed from anterior to posterior, whereas in Cyclestherida and Cladocera differentiation is more synchronous.

CONCLUSIONS

In this study, developmental sequences from representatives of all branchiopod taxa are compared and analyzed using a Parsimov event-pairing approach. The analysis reveals clear evolutionary transformations towards Cladocera and the node of Cladoceromorpha which correspond to distinct heterochronous signals and indicate that the evolution of Cladocera was a stepwise process. A switch from a strategy of indirect development to one of pseudo-direct development was followed by a shift in a number of morphological events to an earlier point in ontogenesis and simultaneously by a reduction in the number of pre-metamorphosis molts. A compression of the larval phase as well as a shortening of the juvenile phase finally leads to a precocious maturation and is considered as a gradual progenetic process.